Battery charging



R T. @HESEMAN BATTER! CHARGING Filed Jan. 4, 1939 .H .w m Q @ad june 2W, 1941.1

. shows the proper Patented June 17, 1941 Ralph T. Cheeseman, Lynn, Mass.,

assigner to General Electric Company, a corporation of New York Anpucatincanuary 4, 1939, serial No. 249,277' 6 Claims. (Cl. 171-95) lI'his invention relates to battery charging and more particularly to an instrument for facilitating the correct adjustment of the charging current cfa storage battery.

A simple and well` known way to charge a 'storage battery` quickly from a substantially constant voltage source is to charge it at Fa pre# determined relatively high rate until it is about ninety per cent charged and then reduce the charging rate to a relatively low nishing value so as not to overheat the battery. During thev relatively high rate the battery voltage is increasing thus causing a tapering ,decrease in charging current. Consequently, at voltage there is a corresponding correct charging current and vice versa.

If a battery were always charged from the same source of constant voltage and if the impedance of thebattery charging circuit were,`

always constant, the circuit could vreadily be adjusted so asto charge the battery at the proper rate regardless of its state of charge. 'However, these ideal conditions are often not realized in practice. For example, some batteries and their chargers on Pullman cars are connected -to power circuits in many diierent cities and the voltages of these circuits are' often quite ydiierent. Furthermore, ,changes in ambient temperature cause changes in the impedanceof the battery charging circuit. Another change in impedance is caused with time, as when copper-oxide charging rectifiers change their resistance as they age.

In accordance with this invention there is provided a novel and 'simple instrument whereby the battery charging circuit can be quickly and easily adjusted to provide the'proper charging current for 'anystate of charge of the battery, or any applied voltage or any impedance condition of the charging circuit.

An object of the invention is t provide a new Hand improved instrument forr facilitating the adjustment of battery charging circuits.

The invention will be better 'understood by reference to the following'description taken in connection with the accompanying drawing and its scope will be pointed out. in the appended claims.

any given battery y meter and a voltmeter.

In the drawing Fig. 1 shows an embodiment of the invention connected to a diagrammatically illustrated battery charging system, and Fig. 2

two-rate'charging characteristic's of a 32-ce1l lead storage battery.

Referring now tothe drawing, there is shown therein an alternating current power circuit-i connected to a-rectier 2 of any suitable type through an adjustable series impedance 3. This impedance may be of any suitable type such as atapped reactor or an ordinary rheostat. The

' direct current output terminals of the rectifier are connected to a storage battery-4 through a lowfrate-of-charge controlling resistor 5. This resistor is normally short circuited by the con-` tacts of 'a voltage relay 6 connected across, the batter'y. This relay is so set that it opens its contacts when the voltage olfr the battery reaches a point corresponding to approximately ninety percent full charge of' the battery.

For facilitating the proper setting of the series impedance 3 there is provided a combination instrument having a casing containing an a'm- The ammeter has terminals connected in the charging circuit by means of a shunt 8 and the voltmeter has terA minals connected across the battery. Thus, the reading of the voltmeter indicates the state of charge ofthe battery, and the reading of the ammeter 'indicates the charging current of the battery. The voltmeter and ammeter scales are juxtaposed and corresponding points thereon are connected by lines 8 so as, in effect, to` form a voltage of about 64 volts corresponding to about 2 volts per cell. At thisrvoltagethe proper charging current is approximately amperes. The 10U-ampere charging current ilowing in the battery increases its state of charge. When the battery voltage has 'risen to about 2.4 volts per cell or 77 volts fory the entire battery, -the relay l operates to insert the resistance 5 i'n the charging circuit, thus reducing the charging rate from about 'i7 amper-es to about 30 amperes. As has been statedabove, this point corresponds to about ninety per cent full charge of the battery andthe remaining'ten per cent ofthe charge is put into the battery. at the relatively low iinishing rate. It will be noted that the points onv the voltmeter and ammeter scales connected by the lines I correspond substantially to thevcoordinates of the pointson the characteristic curve shown in Fig. 2. By means of the instrument 1, the charging 'current of any' battery charger may be adjusted to the proper value for the particular as rapidly as possible without injury to the battery. Without the use of this instrument the battery may be 'charged at a lower rate than it can be charged,v thus'wasting time or it can be charged at a higher rate than the proper rate,

rthus subjecting theA battery to injurious heating and gassing.

While there has particular embodimentof this inven ion, it will be obvious to those skilled in the artt at/various changes and modications can be made therein without departing from the invention and, therefore, it is aimed in thev appended claims to cover all such changes and mo'di'iications asl fall within the true spirit and scope of the invention.

` What I -claim as new and desire to secure by Letters Patent of the United States, is:

1. In a constant voltage taper charging system for storage batteries, an instrument for indicatfor storage batteries, an instrumentfor indicatl ing the"correct chargingeurrent of a storage battery foranyy particular state of .charge thereof comprising.. va casing, a meter for indicating the state of battery charge in terms of battery potential mounted therein,a' second meter for indicating battery charging current mounted therein,

said `meters having pointers cooperating respec-e tively with juxtaposed 'scales on a common scalecarrying member, and lines on said member connec'ing POints on the scale ofthe state-of-charge indicating meter with'points on 'the scale of Ythe charging-current indicating meter', said connected points corresponding substantially to the coordinates of .points on la predetermined battery charging characteristic curve.

' `3. In a constant voltage taper charging system lfor storage batteries, an instrument for indicating the correct charging current of a storage battery for any particular state' of charge thereof comprising, a casing, a meter for indicating the been shown and described astate of the battery being charged so asto bring the battery up to ninety per cent of full chargel state oi' battery charge in terms of battery potential mounted therein, a second meter for indicating ,batteryfcharging current( mounted therein, said meters having their respective pointers s0 arranged that theycoincide when the correct relationx exists between state of charge and charging current. r

4. In a constant voltage taper charging system for storage batteries, an instrument for indicating the correct charging current of a storage battery for. any particular state of charge thereof comprising, a casing, a meterl for lindicating the state of'battery charge in terms of battery p9- tential mounted therein, a second meter for indicating battery charging current mounted therein, said meters having a common scale for their respective pointers so arranged that when said pointers coincide the correct relation exists between rate of charge and charging current.

' 5. -In a constant voltage taper charging system for storage batteries, an instrument for indicating the correct charging current of a storage battery for any particular state of chargethereof comprising, a meter having a movable element Whose position indicates the state of battery charge, and a second meter having a movable element whose position indicates the battery charging current, said meters Jgeing so arranged that the positions of said elements correspond with each other when the correct battery charging current iiows in the battery for its particular state of charge@ 6. In a battery charger which is -selectively connectible to different constant voltage supply circuits having diierent .voltage levels and whichl sive voltmeter and a batterycharging .current responsive' ammeter, the pointer readingY of said voitmeter increasing as charging progresses and` the pointer reading ofsaid ammeter decreasing as charging progresses, and means for so c'orrelating the oppositely varying readings of said meters that the pointers are in eiective registration when the battery charging current is correct for the then existingbattery voltage whereby charging will be completed in the minimum safe time for any particular supply circuit voltage level and initial state of battery charge.

RALPH T. CHEESMAN. 

